Transmission system



I. B'. LEVINE TRANSMISSION SYSTEM Filed March 7, 1936 IE1 G- 1 COMMERCIAL POWER SOURCE I coNsuMERs DWELLING PROGRAM SOURCES LOAD ' Puma-R RECEIVER /5-'- SUBSTATION INVENTOR Irwin B. Levine ATTORNEY FREQUENCY W9. TELEPHUN.

Patented Nov. 16, 1937 TRANSMISSION SYSTEM Irwin B. Levine, New York, N. Y., assignor to Wired Radio, Inc., New York, N. Y., a corporation of New York Application March 7, 1936, Serial No. 67,630

1 Claim.

My invention pertains in general to program distribution systems and specifically relates to systems for the broadcast of programs by carrier frequency energy over power lines.

The principal object of my invention consists in providing compensation means for effecting the uniform distribution of carrier frequency energy to a plurality of consumers served by both commercial power and program signalling energyover common wire transmission lines.

Another object consists in providing a wired radio broadcasting system including compensation means for equalizing attenuation eflects attendant the transmission of carrier frequency energy over a commercial power distribution networ I accomplish these and other desirable objects in a novel compensation system employing transducing network means for effecting equalization of attenuation effects for bringing about uniform and constant conditions of carrier frequency program energy reception by a consumer.

In the drawlngwhich accompanies and forms a part of this specification;

Fig. 1 is a diagrammatic representation of a commercial power distribution network used for wired radio broadcasting purposes in accordance with one embodiment of the system of my invention; and

Fig. 2 is a graphic representation of equalizing compensation effected according to the principles of my invention.

Referring to the drawing in detail and particularly to Fig. 1, power lines I are indicative of a three-phase commercial power distribution network for distributing commercial power as well as carrier frequency program energy to a plurality of consumers connected therewith. The

' power lines I originate at a substation 2 including a commercial power source 3 such as transformer equipment or generation apparatus for supplying commercial alternating current. Program sources I, 5, and. 6 are also provided within the substation 2 for supplying program modulated carrier frequency energy to the power lines I. The program sources 4, 5, and 6 each supply carrier energy at different frequencies for simultaneously transmitting different program channels.

The power lines I connect with a multiplicity of consumers dwellings in the usual manner through secondary transformers. A typical condition is presented in Fig. 1 in which the secondary transformer 8 supplies consumers voltages to the local distribution circuit 1 within the consumers dwelling 9. The local distribution circuit includes a watt-hour meter ill, a service switch II, and fuse-panel l2. In accordance with the principles of my invention, a transducing network I3 is connected in this local distribution circuit ahead of the commercial power load l4 and wired radio receiver IS. The commercial power load i4 is indicative of various commercial current consuming devices such as incandescent lamps, heaters, and the like, while the receiver I is indicative of equipment for selectively receiving and reproducing the programs transmitted at discrete carrier frequencies from the sources 4, 5, and 6.

The transducing network l3 includes a branch I3a across the lines I which at low power frequencies is capacitative and has a high reactive impedance. A branch l3b in series with one side of the lines 1 possesses at low power frequencies only a low value of impedance, and will not therefore, affect the line voltage at the consumers home. The two branches I 3a and l3b may be composed of various forms of circuit elements to produce the desired result, the parameters being determined in accordance with transmission conditions as will be hereinafter apparent.

Referring to Fig. 2, attention will be given to a typical condition of transmission for a program channel. The curve a represents a selected condition for the voltage-frequency transmission for a particular program channel, 0 representing the carrier frequency, while C-f1 represents the lower side band range. The carrier frequency indication coincides with the curve a at a point which is about half of the amplitude of the side band range. In this arrangement, substantially one side band is transmitted, with a small portion of both side bands for the low audio frequency ranges. It will be understood, of course, that other arrangements not departing from the intended scope of my invention may be employed if desired.

My experiments have shown that certain undesirable effects in wired radio transmission are due to attenuation condition existing in the distribution network and which under certain circumstances assumes a definite relationship to the frequencies of the audio range transmitted by the carrier. Dotted line curve b, in Fig. 2, rep-l rier, this attenuation characteristic having a substantially constant decrement away from the carrier frequency. According to my invention, this condition viewed from the consumers dwelling 9 is compensated for by the transducing network I3 having parameters producing an opposite attenuation, as shown by dotted curve cl in Fig. 2. It will be seen that this network attenuates at the higher frequencies of the audio range in the same proportion as the distribution network attenuates the audio range over the low frequencies, the intermediate attenuatin conditions being proportional. The slope of curves b and d" are therefore the same and the resultant reproduced program component at receiver I5 is constant and uniform over a level "e". The effective reproduced audio frequency range, in accordance with my invention, is proportional to the product of the transmission medium characteristics and the transducing network characteristics. The networks disclosed, in effect, operate as a transformer to effect a more efllcient transfer of signalling energy between the power lines and the consumer's receiving circuit. The parameters are such that the transfer of energy is greater for a definite part of the frequency hand than the transfer which would result if the consumers receiving circuit were connected directly to the power lines with this network removed; while, for another part of the frequency band, considered in the present instance to be that part not adjacent the carrier frequency, the transfer of energy is less than would occur with the network removed.

The attenuation effect of the distribution network, indicated by curve b, determines the frequency-reactance characteristic of the network branches I31: and 13b. This attenuation effect is determined by:

(a) Calculation of the attenuation at carrier frequencies of the power lines at each specific receiver location, such calculations being based on electrical line constants which are obtained by computation from knowledge of the physical dimensions and physical properties involved, or

by electrical measurement, or by reference to pertinent statistical data; or

(b) Measurement at each specific receiver location of signals of known frequency and of known amplitude at their origin at the program source.

The method of accomplishing this effect is based primarily upon the circumstance that the line impedance is generally of a rather low value. By putting an inductance in series with the consumers home and then a capacitance between the inductance and the main distribution system the impedance of the consumers home, as viewed from the line, is thereby raised to a considerable degree.

Specifically, this impedance will be:

where Z"=The impedance to which the consumers home is to be raised.

L =The inductance placed in series with the consumers home. C =The capacitance connected across L Z" will have a maximum value at a frequency which may be represented with sufficient accuracy as equation (1) reduces to:

Therefore woL=JR'R and "7-, 00C JR R Over the limited range of frequencies involved, the carrier frequency signal voltage at the input of the wired radio receiver l5 will bear a close relation to the voltage IZ" built upacross the capacitance C. For values of Z" which have no great effect upon the line current I, the signal voltage at the receiver will be very nearly proportional to the value of Z". Z" will vary with frequency, reaching a maximum at and falling continuously as the frequency departs in either direction from this value. Hence, a sloping voltage-frequency characteristic is achieved, and by choosing suitable values of L and C, this characteristic may be varied over a wide range.

It should be noted that, for frequencies at and near the signal voltage at the receiver is actually increased by the use of this network. At the desired optimum frequency of transmission the impedance of the inductance and of the capacitance are each approximately equal to the square root of the product of the original impedance of the home and the higher value to which it is raised.

At the particular optimum frequency the transmission is most efficient; below and above that frequency there is a greater attenuation of the signal. The rate of attenuation is approximately proportional to the value of impedance to which the consumers home is raised and by the proper choice of this impedance any desirable slope of attenuation may be attained.

When more than one carrier frequency is to be transmitted and thefrequency bands are to be equalized each arm of the network consists of more than one element, as is shown in Fig. 1; at each carrier frequency the impedance of the arms is computed on the same basis as for a single channel. At any particular frequency the reactance of the series and shunt arms must be of opposite sign.

Although I have shown a preferred form of my invention, it will of course be recognized that changes will occur to those skilled in the art 179. TELEPHONY.

which will not depart from the intended scope of my invention. I do not, therefore, desire to limit myself to the foregoing except insofar as may be pointed out in the appended claim.

What I claim is new and original and desire to secure by Letters Patent of the United States is:

A transmission system comprising, a commercial power distribution. network, a consumers circuit connected to said network and including a power load and a wired radio receiver, means for impressing program modulated carrier fre- L-A'Lli Iilll'L/i quency energy upon said network, said network, in combination with said consumers load operating to produce a gradient attenuation of said carrier frequency energy, a transducing network connected in said consumers circuit for permitting the passage therethrough of said commercial power while effecting a transducing operation to compensate for said attenuation gradient to effect an increased signal power level of uniform characteristics at said consumers receiver.

IRWIN B. LEVINE. 

